Optical and microstructural studies of InGaN∕GaN single-quantum-well structures

Abstract

We have studied the low-temperature (T=6K) optical properties of a series of InGaN∕GaN single-quantum-well structures with varying indium fractions. With increasing indium fraction the peak emission moves to lower energy and the strength of the exciton–longitudinal-optical (LO)-phonon coupling increases. The Huang–Rhys factor extracted from the Fabry–Pérot interference-free photoluminescence spectra has been compared with the results of a model calculation, yielding a value of approximately 2nm for the in-plane localization length scale of carriers. We have found reasonable agreement between this length scale and the in-plane extent of well-width fluctuations observed in scanning transmission electron microscopy high-angle annular dark-field images. High-resolution transmission electron microscopy images taken with a short exposure time and a low electron flux have not revealed any evidence of gross indium fluctuations within our InGaN quantum wells. These images could not, however, rule out the possible existence of small-scale indium fluctuations, of the order of a few at. %.

Does In form In-rich clusters in InGaN quantum wells?

“…The in-plane extent of these well-width fluctuations is small, typically 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 F o r P e e r R e v i e w O n l y hole confined states decreases by 58 meV. Since kT at room temperature is 25 meV, a monolayer change in quantum well thickness, consistent with electron micrographs, is sufficient to localise the carriers [3].…”

“…High-resolution electron micrographs show that in the InGaN/GaN quantum well system, the lower quantum well interface appears to be atomically abrupt, whereas the upper interface is atomically rough [3]. The in-plane extent of these well-width fluctuations is small, typically 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 F o r P e e r R e v i e w O n l y hole confined states decreases by 58 meV.…”

“…There is clear evidence that, at low temperature, the dominant emission from InGaN/GaN quantum-well structures involves the recombination of strongly localised excitons (see, for example [1][2][3]). Graham et al [3] studied the low temperature (T = 6 K) optical properties of a series of In x Ga 1-x N/GaN single-quantum-well structures where the indium fraction x varied from sample to sample over the range 0.05 -0.25.…”

“…Graham et al [3] studied the low temperature (T = 6 K) optical properties of a series of In x Ga 1-x N/GaN single-quantum-well structures where the indium fraction x varied from sample to sample over the range 0.05 -0.25. The structures were grown by Metal Organic Vapour Phase Epitaxy (MOVPE), and the InGaN quantum well was 2.5 nm thick.…”

Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells

“…The optical properties of the structures were studied by measuring the photoluminescence (PL) spectra as a function of temperature, and the PL decay transients at 10 K. The samples were mounted on the cold finger of a temperature controlled closed-cycle helium cryostat and inclined at Brewster's angle with respect to the collection axis to minimise the effects of Fabry-Pérot interference oscillations on the PL spectra [15]. For the temperature dependent PL measurements, a CW He/Cd laser with a photon energy of 3.815 eV was used as the excitation source.…”